G8 inverter problems

[Nickd]

First post, be gentle!
We've an 8.6 kWp setup with Tesla PW2. Until recently we had a Fox 5 kW inverter, despite the installer saying an 8 kW would be installed. That was rectified last Wednesday, since which time I've seem some weird behavior.

Everything is fine until the amount of solar generated approaches our DNO export limit of 5.5 kWh. At this point, the inverter 'clicks' and the wattage which might have been around 5700 drops to zero. The inverter then counts down from 60s to zeros. It then 'thinks' and 'clicks' for about 20s and then the 0W figure gradually increases. At no point has the sun diminished or a cloud come in, conditions remain unchanged.

This repeats, the cycle takes 200s consistently, the Watts never gets back to anywhere near the true figure until later in the day where the panels are generating maybe 4 ish kWh. The installer is due back next week, but I am wondering has anyone with a Fox inverter observed similar? Thanks in advance

[Dave Foster]

At 8kW I assume it’s a KH8 that has been installed ?

That sounds very much like it is seeing either a high grid voltage or too high a current on one of the PV strings which results in an alarm that shuts down the generation - the inverter will then go through a mandatory wait time and then perform checks before finally restarting.

You should be able to see a log of the alarms at the inverter panel by looking in History, Error Logs which will tell you the error codes generated (please post them here) and that will dictate the next steps to fix it.

Hopefully it’s nothing too complex for the installer to resolve for you.

[Nickd]

Thanks for the quick reply. The A5 sized label on the side says G8, so I am not sure it is KH8...By pressing the fingerprint button on the front I can get this:
0 GridVoltFault 12/05/2024 12:08. This is exactly the time the error started today. Nothing more recent than this is logged. I think the 0 simply indicates it is the most recent error. I didn't see a History option. This was under Error codes.

We do suffer from over voltage....with DNO for the last 8 months. The strange thing is that, taking today as an example, the error lasted from 12:08 to 3pm but I only have that single error recorded today. And if I look at the 'Vac' as the inverter shows it, it is consistently 254 and above now, which is the same it was when the error happened.

Previous errors include VGridTransient and GridFreqFault

[Dave Foster]

Ahhh ok sorry my bad, I was thinking it was a hybrid inverter, but it’s a PV inverter (G series).

254V is high, the maximum permissible grid voltage is 253V but inverters often measure several volts higher particularly when they are nearing maximum power - if this is reported to your DNO they should attach logging equipment to your incoming line to check what the voltage is across a several day period, if it is high they may then change the tap on the local transformer to reduce the voltage at your home - but it is complex and depends on a number of factors.

It may be your installer can set your grid voltage trip limits to be a little bit higher on the inverter to avoid this, but it may also require your DNO to attend and rectify as well depending on what grid limits reach.

[Nickd]

Yes DNO already logged the voltage for a week and concluded there was a problem. They said that they'd make a tap change but 8 months later...nothing. Hopefully the installer can tweak as you suggest.

[Nickd]

Installer due tomorrow. I am sure it is the over voltage problem. It ran at 254, 255 even 256 between 10am and 4pm today, where essentially the inverter was always restarting. But bizarrely it then ran at 258 even 259 quite happily. It is beyond me, the only difference is that by the time it was at 258 or 259, somewhat less wattage was being produced.

[Will]

Sounds like the DNO can just tap it down slightly at the sub station and you'll be fine or you may need a voltage optimiser installed for your property. Please keep us updated.

[Nickd]

The installer attended today. Winced at the voltage level. Spent no more than five minutes configuring the inverter such that it is happy at higher voltages. Now all I need is some sun! Time to chase my complaint with the DNO, who have known about this for eight months and done nothing.

[Dave Foster]

The installer attended today. Winced at the voltage level. Spent no more than five minutes configuring the inverter such that it is happy at higher voltages. Now all I need is some sun! Time to chase my complaint with the DNO, who have known about this for eight months and done nothing.

Hopefully that should allow you to output at maximum power now, it's a good idea to chase your DNO - they may have changed the transformer tap last time - you usually see approx 5V - 7V per tap change... the problem (expense) comes when they run out of taps on it... fingers crossed.

[Nickd]

The installer just called, they rang the DNO and said customer has lots of expensive kit, if this problem you have known about for months breaks anything it is going to cost you guys. I am now supposed to hear from them today. Which is nice as they haven't responded to my complaint yet and have 5 hours left to do so.

[Nickd]

Sadly, the issue continues. Once yesterday, but repeatedly today from roughly midday. What is worse, the voltages today are not high at all, certainly well below the upper limit set by the installer when they visited earlier this week.

[Nickd]

Well, the problem has changed, but not for the better.
The inverter now just has a red exclaimation mark and the words 'Meter Fault'. The export meter has no red lights on, but is showing the lifetime generation figure. I've followed the instructions to turn AC then DC and wait 5 minutes but no change.

[Dave Foster]

I’m sorry to hear you’ve been having continued problems - It sounds as if the inverter has been fitted with either a meter or CT clamp to measure the loads and it sounds as if that has a problem.

If it has a CT clamp it is a small white clip on cable clamp that is usually connected at the incoming meter on the live feed. It is cabled back to the inverter and connects to the meter connector underneath the inverter - to generate this fault it would need the cable to have been broken (open circuit), it sometimes happens at the connector on the inverter if the cabling has been disturbed and there is no strain relief.

If it has a meter fitted (usually a Chint or Eastron) it would be fitted near the incoming feed, sometimes near the breaker - again it is cabled back to the inverter and connects in the same ‘meter’ connector under the inverter.

If nothing has been disturbed and there are no obvious signs of damage anywhere - as you have already power cycled the inverter, i’m afraid to say the only advice I can offer is to call your installer as it’s going to need some fault finding and possible a replacement meter/CT clamp depending on what has been fitted.

[Nickd]

Thanks for your reply. I don't see a CT clamp as you describe but there is an emlite meter which has been in place from the start ( install complete Feb 2024 but incorrect 5kW inverter fitted). It shows a solid red light. Back to the installer I go!

[Dave Foster]

I don’t think it’s the emlite meter - they are pretty dumb generation meters, there must be a meter fitted somewhere else or the inverter genuinely has a fault ?.

[Nickd]

I suppose there is the Kaifa Smart meter, which was originally for import only. The installers are of the opinion is is related to the over voltage issues we have. But current voltages are just fine and still this Meter Fault. And the old inverter managed for 2+ months. Bit underwhelmed really. I tried ringing Fox UK but it says installer only, send us an email.

[Nickd]

Wow, I emailed Fox UK and got this answer
"This is a settings issue we have now changed the setting on your inverter and it is operating as it should be now however if you have any other problems it may be worth contacting your installer as some issue we won't be able to resolve them remotely like we have done in this instance"

Just like that, and it is working, for now at least. They answered within 3 hours of me emailing!

[Dave Foster]

Wow, I emailed Fox UK and got this answer
"This is a settings issue we have now changed the setting on your inverter and it is operating as it should be now however if you have any other problems it may be worth contacting your installer as some issue we won't be able to resolve them remotely like we have done in this instance"

Just like that, and it is working, for now at least. They answered within 3 hours of me emailing!

Great response from them, it sounds as if you were correct you don’t have a meter fitted - they tend to be used where there is an export limit set by the DNO but in your case it sounds like it was left enabled when it shouldn’t have been.

Nice one… we can only hope that your DNO fixes the supply voltage that quickly

[Nickd]

Ha, the DNO will fix the problem 27th June. That is a year since I contacted them!

[Nickd]

All the Fox change really achieved was to get rid of the Meter Fault error. Now, between about 10am and 4pm we get continuous inverter reboots, initially after a GridVoltFault error. This is at 256V as shown on the inverter, despite the installer saying they had upped the limit above that.

[Dave Foster]

If you do have a CT clamp fitted, it’s most likely you have a cable break - and if there hasn’t been any work done near the cable run, the most likely place for it to fail is at the connector under the inverter itself - the multi core cables tend to snap inside the connector where the screw crushes the cable.

If you have an export limit set the inverter won’t be able to limit it’s output and wont report the house load correctly but other than that it should function correctly.

The problem with the high voltage is that there are multiple safeties in the inverter to guard against over voltage, your installer may have raised one but the others may still be tripping - these aren’t averaging faults and will trip the inverter if they exceed the limits for only a short duration which I suspect is what is happening.
It sounds from what you have said that your DNO must have a more significant piece of work to reduce your voltage, if it had been a simple tap change they would have done it, so likely an entire transformer change or similar upstream from you.

It’s not a great solution but if you can apply load in the house during the peaks which will be more likely to be mid morning and mid afternoon, then it will significantly reduce the voltage and hopefully avoid a trip - it’s not the best but turning on a water heater, a heat pump, a cooker, radiator would help.

[Nickd]

There is no CT clamp, I don't know why. Similarly there is no power meter, just an Emlite. I asked the installer to limit export to 3kW but although he set it on the inverter it had no effect as, in his words, I don't have any grid monitoring. Fox were supposed to be looking at it today.
I ran the immersion to see what effect if any there was on voltage. It did drop, not enough though. The inverter struggles between 9am and 5pm currently, so not really a solution. Thanks for your reply, anyway. Oh yes, DNO clearly said a tap change, nothing more involved.

[Nickd]

CT clamp fitted, tap change done (20 minutes!) So far so good. Just need some sun!